It is proposed to investigate the effect of energy restriction on the utilization of protein in both the normal and the malnourished rat. Methods will involve nitrogen retention in the growing animal, nitrogen balance in the adult and measurement of hepatic microsomal enzymes at various stages throughout life. Diets will be varied in the source of protein and in the degree of energy restriction. The abnormal malnourished animals will be obtained by dietary restriction of the dams subsequent on conception and during lactation and of the pups after birth.